Typical connection structures that prevent portions connecting connectors to connection targets from becoming wet with water are known. One such example is a structure in which a housing that holds a connector is engaged with an adapter that is secured to a connection apparatus including a connection target so as to cover the connection target. With this structure, the connector is connectible to the connection target while ensuring that waterproofness is maintained. Japanese Laid-open Patent Publication No. 2009-109578 and No. 2009-294343 discuss a typical waterproof technology as described above. The length of the connection target in the axial direction of the connector may vary depending on the type of the connection target, and the position of the connection portion where the connector and the connection target are connected to each other may vary depending on the type of the connection target. In a connection as described above, separate types of connection components are typically prepared corresponding to the types of the connection targets.